With the comprehensive implementation of prevention and control measures for endemic fluorosis and endemic arsenicosis in China, and in accordance with the World Health Organization (WHO) recommended drinking water standards and the Chinese standards of allowable daily fluoride intake and limit values of arsenic content in drinking water, Chinese residents have entered the era of low-dose fluoride and arsenic exposure. However, there have been few studies focused on the long-term health effects of exposure to low-dose fluoride and arsenic both domestically and internationally. Further more, study on non-target organs of fluoride and arsenic has been neglected. The conclusions are also inconsistent, and there is an urgent need for systematic study to clarify them. Accordingly, this paper proposes to establish a cohort of people exposed to low-dose fluoride and arsenic, systematically carry out study on the long-term health effects and mechanisms of low-dose fluoride and arsenic exposure, and promote China's prevention and control experience to the "the Belt and Road" countries, in order to provide a scientific basis for the formulation of prevention and control strategies and measures for endemic fluorosis and endemic arsenicosis under the new situation in China.

Objective:To investigate the relationship between plasma fluoride content, daily calcium intake and blood cell parameters in children and adolescents.Methods:This study was based on the National Health and Nutrition Examination Survey (NHANES) database of the United States from 2013 to 2016, with 3 684 children and adolescents aged 6 - 19 as the research subjects. Information on plasma fluoride content, daily calcium intake and blood cell parameters from the database were collected. Non-linear relationships between plasma fluoride content, daily calcium intake and blood cell parameters were analyzed using restricted cubic splines. If there was a non-linear relationship, the optimal inflection point was calculated using threshold/saturation effect analysis method. Subsequently, multiple linear regression models were used to analyze the associations among the three, and the modification effect of daily calcium intake (binary classification, stratified by median daily calcium intake) on the association between plasma fluoride content and blood cell parameters was analyzed.Results:There was no non-linear relationship between plasma fluoride content and white blood cell count, hemoglobin content and platelet count ( Pnon-linear > 0.05), but there was a non-linear relationship between plasma fluoride content and erythrocyte count and hematocrit ( Pnon-linear < 0.001). After adjusting for confounding factors, the optimal inflection points of the effects of plasma fluoride content on erythrocyte count and hematocrit were 0.54 and 0.31 μmol/L, respectively. There was no non-linear relationship between daily calcium intake and blood cell parameters ( Pnon-linear > 0.05). After adjusting for confounding factors, for every 1 μmol/L increase in plasma fluoride content, the white blood cell count increased by 0.49 × 10 9/L ( P = 0.009). There was a saturation effect in the association between plasma fluoride content, erythrocyte count and hematocrit: when plasma fluoride content was < 0.54 μmol/L, the erythrocyte count decreased by 0.46 × 10 12/L for every 1 μmol/L increase ( P < 0.001). When plasma fluoride content was < 0.31 μmol/L, the hematocrit decreased by 6.29% for every 1 μmol/L increase ( P = 0.006). The above associations were not statistically significant when plasma fluoride content was higher than the optimal inflection points ( P > 0.05). After stratification according to the median daily calcium intake, in the low-calcium group (daily calcium intake < 0.87 g), for every 1 μmol/L increase in plasma fluoride content, the white blood cell count increased by 0.77 × 10 9/L ( P = 0.001). When plasma fluoride content was < 0.54 μmol/L, the erythrocyte count decreased by 0.41 × 10 12/L for every 1 μmol/L increase ( P = 0.002). When plasma fluoride content was ≥0.54 μmol/L, erythrocyte count decreased by 0.47 × 10 12/L for every 1 μmol/L increase ( P < 0.001). When the plasma fluoride content was < 0.31 μmol/L, the hematocrit decreased by 8.29% for every 1 μmol/L increase ( P = 0.011). The above associations were not statistically significant in the high-calcium group (daily calcium intake ≥0.87 g, P > 0.05). There was an interaction of daily calcium intake and plasma fluoride content on platelet count ( Pinteraction = 0.070), as demonstrated by an increase in platelet count of 12.68 × 10 9/L ( P = 0.013) in the low-calcium group and a decrease in platelet count of 9.05 × 10 9/L ( P = 0.035) in the high-calcium group for every 1 μmol/L increase in plasma fluoride content. Conclusions:The blood cell parameters of children and adolescents are closely related to plasma fluoride content, but not directly related to daily calcium intake. However, the correlation between plasma fluoride content and blood cell parameters varies among different calcium intake populations, and daily calcium intake can modify the association between plasma fluoride content and platelet count.

Objective:To investigate the effect of melatonin (MEL) on learning and memory abilities of fluoride-exposed offspring rats and the role of gut microbiota.Methods:Twelve 8-week-old Sprague-Dawley (SD) rats (8 females and 4 males) with a body weight ranging from 180 to 220 g were selected and divided into control group 1 and fluoride-exposed group 1 using a random number table method, with 6 rats in each group (female ∶ male = 2 ∶ 1). They were free to drink purified water or purified water containing 100 mg/L sodium fluoride, respectively. After 2 months, male and female rats were raised together in cages, and the first postnatal day (PND) of the offspring rats was recorded as PND0. In PND21, the offspring rats of fluoride-exposed group 1 were divided into fluoride-exposed group (Group F, n = 6) and fluoride + MEL group (Group FM, n = 6) using a group design, and continued to be exposed to fluoride through drinking water. The offspring rats of control group 1 were divided into control group (Group C, n = 6) and MEL group ( n = 6). The groups FM and MEL were given 20 mg/kg MEL by gavage, while the groups C and F were given the same dose of normal saline by gavage. In PND60, novel object recognition and Morris water maze tests were used to observe the learning and memory abilities of the offspring rats. Western blotting (WB) was used to detect the expression level of brain derived neurotrophic factor (BDNF) in the hippocampus of the offspring rats. And 16S rDNA sequencing technology was used to detect the changes in the structure and composition of gut microbiota in fecal samples. Results:The results of novel object recognition test showed that there was a statistically significant difference in the discrimination index (DI) among the four groups of offspring rats ( F = 3.95, P = 0.024). The DI in groups C and FM was higher than that of Group F ( P < 0.05). The results of Morris water maze test showed that compared with Group C, the platform-crossing time of the offspring rats of Group F were less and they had a longer time to reach the platform for the first time ( P < 0.05). Compared with Group F, the platform-crossing time of the offspring rats of Group FM were increased and they had a shorter time to reach the platform for the first time ( P < 0.05). The WB results showed that compared with Group C (1.00 ± 0.07), the expression level of BDNF protein in Group F (0.68 ± 0.26) was lower ( P < 0.05). Compared with Group F, the expression level of BDNF protein in Group FM (0.99 ± 0.14) was higher ( P < 0.05). Anosim similarity analysis showed significant differences in the structure and composition of gut microbiota in the four groups of offspring rats ( R = 0.395 062, P = 0.002). The distribution characteristics of gut microbiota species showed that at the phylum level, compared with Group C, the relative abundance of Bacteroidetes in Group F increased from 14.26% to 37.00%, and the relative abundance of Firmicutes decreased from 68.78% to 45.95%. Compared with Group F, the relative abundance of Firmicutes in Group FM increased from 45.95% to 65.26%, and the relative abundance of Bacteroidetes decreased from 37.00% to 23.00%. At the genus level, compared with Group C, the relative abundance of Lactobacillus, Dubosiella, HT002 and UCG-005 in Group F was lower, while the relative abundance of unclassified Muribaculaceae was higher. Compared with Group F, the relative abundance of Lactobacillus, Dubosiella, HT002 and UCG-005 in Group FM was higher, while the relative abundance of unclassified Muribaculaceae was lower. The results of linear discriminant analysis revealed that the Candidatus-Saccharimonas and Incertae-Sedis were significantly enriched in Group C, unclassified Muribaculaceae and Muribaculum were significantly enriched in Group F, and Allorhizobium- Neorhizobium- Pararhizobium- Rhizobium were significantly enriched in Group FM. Conclusion:MEL can improve the learning and memory impairment of offspring rats induced by fluoride exposure by changing the structure and composition of gut microbiota.

Objective:To study the effects of fluoride on apoptosis and oxidative stress levels of spinal cord nerve cells in rats.Methods:A total of 54 6-week-old Sprague-Dawley female rats, weighing 150 - 200 g, were selected and fed for 1 week. They were divided into a control group [given deionized water containing 0 mg/L sodium fluoride (NaF)], a low fluoride group (given deionized water containing 50 mg/L NaF), and a high fluoride group (given deionized water containing 100 mg/L NaF) using a random number table method, with 18 rats in each group. All groups received standard feed. After 4, 8, and 12 weeks of fluoride exposure, six rats were selected from each group to observe the occurrence of dental fluorosis, and the motor function of hind limbs in rats was evaluated based on the Basso-Beattie-Bresnahan (BBB) score. Then the rats were anesthetized with 5% chloral hydrate via intraperitoneal injection and euthanized by cardiac puncture. Spinal cord tissue of the rats was collected to detect the activities of oxidative stress factors such as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), as well as the contents of malondialdehyde (MDA) and catalase (CAT). After 12 weeks of fluoride exposure, morphologic changes in rat spinal cord neurons were observed using Nissl staining, and apoptosis of spinal cord nerve cells was detected using the TdT mediated dUTP nick end labeling (TUNEL) cell apoptosis detection kit. The Western blotting was used to detect the expression of B-lymphoblastoma-2 (Bcl-2) gene related X protein (Bax), Bcl-2 promoter (Bad), and Bcl-2 protein in rat spinal cord tissue; immunofluorescence staining was used to observe the expression of Bax and Bcl-2 protein in spinal cord neurons.Results:After 12 weeks of fluoride exposure, rats in both the low fluoride and high fluoride groups developed varying degrees of dental fluorosis; the differences of BBB scores of rats in the control, low fluoride, and high fluoride groups were statistically significant ( F = 14.09, P < 0.001). The differences of SOD [(124.04 ± 4.87), (96.66 ± 15.01), (91.12 ± 15.87) U/mg prot] and GSH-Px activitives [(561.92 ± 59.65), (456.83 ± 29.51), (385.07 ± 74.87) U/mg prot], MDA [(9.96 ± 1.50), (16.64 ± 2.05), (20.80 ± 3.37) nmol/mg prot] and CAT contents [(8.97 ± 1.05), (6.39 ± 0.97), (6.42 ± 0.83) nmol/mg prot] among the control, low fluoride, and high fluoride groups were statistically significant ( F = 11.17, 14.19, 30.12, 14.52, P < 0.05). Among them, the SOD, GSH-Px activities, and CAT content in the low fluoride and high fluoride groups were lower than those in the control group, while the MDA content was higher than that in the control group ( P < 0.05). The GSH-Px activity in the high fluoride group was lower than that in the low fluoride group, and MDA content was higher than that in the low fluoride group ( P < 0.05). The intact neuronal structures and clear visible nuclei were seen, and Nissl bodies were uniformly stained in the spinal cord neurons of the control group rats, with more numbers, and no apoptotic cells were observed; the staining of Nissl bodies in the spinal cord neurons of rats was uneven in the low fluoride and high fluoride groups, with fewer numbers, and more apoptotic cells. There were statistically significant differences in the apoptosis rate of spinal cord nerve cells and the expression levels of Bax, Bad, and Bcl-2 protein in the spinal cord tissues of rats in the control, low fluoride, and high fluoride groups ( F = 272.81, 35.53, 17.57, 92.50, P < 0.05). The results of immunofluorescence staining showed that there were statistically significant differences in the fluorescent intensity of Bax and Bcl-2 proteins in the spinal cord neurons of rats in the control, low fluoride, and high fluoride groups ( F = 12.67, 22.14, P < 0.05). Conclusion:Chronic fluorosis induces a decrease in antioxidant enzyme activity, an increase in lipid peroxidation levels, and an increase in neuronal apoptosis in the spinal cord of rats.

Objective:To study the relationship between adult fluoride exposure and grip strength in rural areas of China with fluorosis, as well as the roles of basal metabolic rate (BMR) and body fat percentage (BFP) in the association between fluoride exposure and grip strength.Methods:From April to May 2017, a cluster sampling method was used to conduct a questionnaire survey, physical examination, and biological sample collection on residents aged 18 - 60 in Tongxu County, Kaifeng City, Henan Province (epidemic areas of drinking-water-borne fluorosis). A total of 1 168 subjects were included in the study, including 427 males and 741 females. The fluoride ion selective electrode method and the picric acid method were used to determine the concentrations of urine fluoride and urine creatinine, and the adjusted urine fluoride concentration (CUF) was calculated. BMR and BFP were measured by a bioelectrical impendence method, and the grip strength was measured by a Jamar grip dynamometer. The relationship between CUF, BMR, BFP and grip strength were analyzed using a generalized linear model regression. The mediation effect model was used to assess the mediating effect of BMR and BFP on the association between CUF and grip strength.Results:Female grip strength decreased by 0.28 kg ( P = 0.043) for every 1.00 mg/L increment in CUF. No similar association was found between the two in males ( P = 0.744). Regardless of gender stratification, BMR was positively correlated with grip strength ( P < 0.001). For every 1.00% increase in BFP, female grip strength decreased by 0.18 kg ( P = 0.043). The mediation effect model analysis results showed that the mediation effect ratios of BMR and BFP in the association between CUF and grip strength in female were 65.1% ( P < 0.001) and 8.4% ( P = 0.111), respectively. Conclusion:Fluoride exposure is associated with changes in female grip strength, and BMR changes play a partial mediating role in the association between fluoride exposure and female grip strength.

Objective:To investigate the distribution of physical and chemical water improvement areas of drinking water-borne endemic fluorosis in Inner Mongolia Autonomous Region, as well as the use of household water purifiers.Methods:From April to October 2021, a survey was conducted in a drinking water-borne endemic fluorosis areas in Inner Mongolia Autonomous Region where physical and chemical water improvement was carried out. The survey included the basic situation of the affected villages (number of permanent households, number of permanent residents, historical water fluoride content) and the use of residential water purifiers. Household peripheral water samples were collected to test the water fluoride content. Water purifier installation rate, normal usage rate, qualified water fluoride rate in normal usage, and the proportion of households covered by filter replacement departments were calculated.Results:In Inner Mongolia Autonomous Region, the physical and chemical water improvement areas of drinking water-borne endemic fluorosis were distributed in 2 735 villages in 11 leagues (cities) throughout the region, with 192 950 permanent households and 540 216 permanent residents. The average historical water fluoride content in all leagues (cities) was 2.18 mg/L, and the current average water fluoride content was 0.40 mg/L. A total of 134 763 water purifiers were installed, with an installation rate of 69.84% (134 763/192 950). A total of 10 773 households were surveyed, with 10 396 households using water purifiers normally and a normal usage rate of 96.50% (10 396/10 773). Among them, 10 158 households had qualified water fluoride of normal usage, with a qualified water fluoride rate of 97.71% (10 158/10 396). Of the 10 396 households using water purifiers normally, 3 974 households (38.23%) had filter cartridges used within one year, and 3 961 households had qualified water fluoride, with a qualified rate of water fluoride of 99.67% (3 961/3 974). Six thousand four hundred and twenty-two households (61.77%) had filter cartridges used for more than one year, with 6 197 households had qualified water fluoride and a qualified rate of water fluoride of 96.50% (6 197/6 422). There was a statistically significant difference in the qualified rate of water fluoride between purifiers with different filter cartridge usage times (χ 2 = 110.73, P < 0.001). Among the 10 773 surveyed households, the filter cartridges replacement department covered 10 470 households, accounting for 97.19% (10 470/10 773). Conclusions:In Inner Mongolia Autonomous Region, the physical and chemical water improvement areas of drinking water-borne endemic fluorosis are widely distributed, and the normal usage rate of household water purifiers is relatively high. The qualified rate of water fluoride in household water purifiers with filter cartridges used for more than one year is low.

Objective:To investigate the control situation of drinking water-type endemic fluorosis (hereinafter referred to as drinking water fluorosis) in Xinjiang Production and Construction Corps (hereinafter referred to as the Corps), identify weak links in prevention and control, and provide reference for precise prevention and control of drinking water fluorosis in the Corps.Methods:Monitoring data of drinking water fluorosis areas in the Corps from January to December 2022 were collected from the Corps Center for Disease Control and Prevention, the level of fluoride in drinking water and the prevalence of dental fluorosis in children aged 8 - 12 were analyzed retrospectively.Results:In 2022, the qualified rate of water fluoride in the disease affected TuanChang of the Corps was 100.00% (62/62), and the qualified rate of water fluoride in the disease affected company was 99.44% (705/709). The prevalence of dental fluorosis in children aged 8 - 12 in the disease affected TuanChang was 3.38% (1 412/41 714), and there was no statistically significant difference in the prevalence of dental fluorosis among different age groups (χ 2 = 6.07, P = 0.194). The prevalence of dental fluorosis in children aged 8 - 12 in the TuanChang where the company with water fluoride exceeding standard was located (6.00%, 106/1 768) was higher than that in the TuanChang where the company with qualified water fluoride was located (3.27%, 1 306/39 946, χ 2 = 38.47, P < 0.001). Conclusion:In 2022, the drinking water fluorosis in the Corps has reached the control standard, but attention still should be paid to the water improvement situation and maintenance of water improvement projects in some water fluoride exceeding standard companies, in order to prevent sustained dental fluorosis damage to children in the affected areas, and consolidate the achievements of prevention and control.

Objective:To investigate the iodine nutritional status of children and the consumption condition of non-iodized salt in Henan Province after implementation of the new standard of "Definition and demarcation of water-borne iodine-excess areas and iodine-excess endemial areas" (GB/T 19380-2016, hereinafter referred to as new standard) for four years (2021), and to provide a basis for scientific adjustment of intervention strategies.Methods:In 2021, according to the requirements of the new standard and based on the results of the water iodine survey in Henan Province from 2017 to 2020, a survey was conducted on the iodine nutrition status of children in water-borne high iodine areas in 47 counties (cities, districts, hereinafter referred to as counties) with high iodine administrative village (neighborhood committee, hereinafter referred to as administrative village). In each county, 5 administrative villages with median water iodine > 100 μg/L were selected as the investigation villages, and water samples were collected to determine the water iodine value. Forty non-boarding students aged 8 - 10 (age balanced, half male and half female, age increased to 6 - 12 when less than 40) were selected from each village as investigation subjects. Salt samples from their homes and urine samples were collected to detect salt iodine and urine iodine content, and thyroid volume of children was measured. And the monitoring results of areas where the supply of iodized salt had been suspended for less than 4 years (in newly high iodine areas) and more than 10 years (in previously high iodine areas) were further compared and analyzed.Results:A total of 257 administrative villages in the province were monitored, and the range of water iodine was 1.6 - 609.5 μg/L, with a median of 132.5 μg/L. A total of 8 611 children were tested for salt iodine, urine iodine and thyroid volume. The non-iodized salt rate was 58.3% (5 017/8 611), and the median urine iodine was 342.2 μg/L, thyroid enlargement rate was 2.9% (250/8 611). The median water iodine (153.0 vs 118.4 μg/L), the median urine iodine in children (371.6 vs 287.7 μg/L) and the goiter rate [3.8% (211/5 537) vs 1.3% (39/3 074)] in the newly high iodine areas were higher than those in the previously high iodine areas, and the differences were statistically significant ( Z = 583.12, - 14.09, P < 0.001; χ 2 = 44.40, P < 0.001); the non-iodized salt rate was lower than that of the previously high iodine areas [37.2% (2 057/5 537) vs 96.3% (2 960/3 074)], and the difference was statistically significant (χ 2 = 2 841.37, P < 0.001). Conclusions:The iodine nutrition level of children in water-borne high iodine areas of Henan Province in 2021 is at an excess level, but the non-iodized salt rate in residential households is low. We should make every effort to ensure the precise supply of non-iodized salt in high iodine areas after implementation of the new standard, and strengthen iodine nutrition monitoring and health education for key populations to prevent the occurrence of high iodine hazards.

Objective:To investigate the iodine nutritional status of pregnant women in Hangzhou City and analyze its influencing factors, in order to provide a basis for guiding pregnant women in Hangzhou City to supplement iodine scientifically.Methods:A stratified random sampling method was used to conduct a questionnaire survey on 1 400 pregnant women in Hangzhou City from March to October 2018. Random urine samples and household salt samples from pregnant women were collected, and the levels of urine iodine and salt iodine were measured using arsenic cerium catalytic spectrophotometry and direct titration, respectively. The iodine nutritional status of pregnant women with different basic characteristics and dietary levels were analyzed and compared (Kruskal-Wallis test), and the main influencing factors affecting the urinary iodine concentration level of pregnant women were identified (the ordinal multiple classification logistic regression analysis).Results:The median urinary iodine of pregnant women was 135.00 μg/L, and the qualified iodized salt consumption rate of pregnant women was 83.36% (1 167/1 400). In terms of basic characteristics, there were statistically significant differences in the distribution level of urine iodine among pregnant women with different pregnancy frequency, delivery frequency, and natural abortion frequency ( P < 0.05). In terms of diet, the frequency of consuming milk, yogurt, meat, and whether pregnant women consumed cabbage and cauliflower showed statistically significant differences in urinary iodine distribution levels ( P < 0.05). Ordinal multiple classification logistic regression analysis showed that the urine iodine levels of pregnant women who were pregnant twice were higher than those who were pregnant ≥3 times ( OR = 1.64, P = 0.003). Pregnant women who never or occasionally consumed yogurt had lower urine iodine levels than or equal to those who consumed 2 bottles of yogurt per day ( OR = 0.53, P = 0.044). Pregnant women who never or occasionally consumed meat and those who consumed meat once a week had higher urinary iodine levels than that who consumed meat ≥2 times per week ( OR = 1.40, 1.47, P < 0.05). Conclusions:The overall iodine nutrition of pregnant women in Hangzhou City is at an deficiency level. Pregnancy experience and dietary level are influencing factors on iodine nutrition of pregnant women. It is necessary to carry out in-depth health education for pregnant women, improve the dietary structure during pregnancy, and improve the abnormal iodine nutrition of pregnant women.

Objective:To investigate the iodine nutrition status of key population in Fuzhou City, and to provide scientific basis for adjusting intervention strategies.Methods:From March to October 2021, a survey was conducted on iodine nutrition status of key population in 12 counties (cities, districts) of Fuzhou City. Each county (city, district) was divided into 5 sampling areas according to the east, west, south, north and middle directions. One township (street) was selected from each area, and 40 non-boarding children aged 8 - 10 (age balanced, half male and half female) from one primary school and 20 pregnant women (early, middle and late pregnancy balanced) were selected as survey subjects. Household salt samples and random urine samples were collected, and the salt iodine and urine iodine levels were tested by direct titration and arsenic and cerium catalytic spectrophotometry, respectively. Children's thyroid volume was measured by B-ultrasonography. At the same time, in cooperation with Fuzhou Maternal and Child Health Hospital, the thyroid stimulating hormone (TSH) testing results of heel blood of full-term natural delivery newborns in Fuzhou City in 2021 were collected.Results:A total of 2 400 children were monitored for salt iodine, urine iodine and goiter. The median salt iodine was 24.40 mg/kg, with an iodine salt coverage rate of 93.04% (2 233/2 400), a qualified rate of iodized salt of 97.40% (2 175/2 233), and a consumption rate of qualified iodized salt of 90.62% (2 175/2 400). The median urine iodine was 181.47 μg/L. The rate of goiter was 1.04% (25/2 400). A total of 1 200 pregnant women were monitored for salt iodine and urine iodine. The median salt iodine was 24.10 mg/kg, the coverage rate of iodized salt was 91.08% (1 093/1 200), the qualified rate of iodized salt was 97.90% (1 070/1 093), and the consumption rate of qualified iodized salt was 89.17% (1 070/1 200). The median urine iodine was 128.10 μg/L. The median TSH level in the heel blood of 14 242 newborns was 3.38 mU/L, and the proportion of TSH level > 5 mU/L was 30.96% (4 410/14 242).Conclusions:In 2021, children in Fuzhou City are at an appropriate level of iodine, but pregnant women are insufficient of iodine. We should continue to maintain comprehensive prevention and control measures mainly based on salt iodization, provide health education for pregnant women, and strengthen monitoring of TSH level in newborns.